Aladar jpacz



Patented Mar. 8, 1932 UNITED STATES PATENT OFFICE,

ALADAR PACZ, F CLEVELAND, OHIO, ASSIGNOR TO ALUMINUM COMPANY OF AMERICA, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA PROCESS FOR MODIFYING ALUMINUM ALLOYS CONTAINING SILICON No Drawing. Application filed August 17, 1931, Serial No. 557,733, and in Germany November 20, 1930.

divided and dispersed form. One method of obtaining this result is by adding to the al: loy an alkali metal or the salt of an alkali metal which will react with the molten metal.

to form an alkali metal. Among such salts which have been successfully used in the modification of aluminum base alloys containing silicon are the alkali metal fluorides, hydroxides, peroxides, carbonates, and chlorides.

Ithas been found that the process of modifying aluminum-silicon alloys by adding to the alloy in' the molten form an alkali metal or the salt of an alkali metal has certain disadvantages, one of which is the fact that during the modification process gas appears to segregate readily in the metal, with the result that the final casting is often very porous. For this reason, it has been necessary heretofore to carefully control the amount of alkali metal or alkali metal salt added to the molten alloy.

The principal object of this invention is to provide a new method of modifying the structure of aluminum base alloys containing silicon which method is simple, easily controlled in the foundry, and free from the disadvantages herei'nabove mentioned as incident to the known processes of modification which comprise the addition of alkali metal.

A further object of my invention is the provision of a method of modifying the structure of aluminum base alloys containing silicon, which method makes possible the addition of large amounts of an alkali metal modifying agent but avoids the production of highly porous castings.

I have discovered that the known methods of modifying aluminum base alloys containing silicon by addition to a melt thereof of an alkali metal or a substance which produces alkali metal, such as the salt of an alkali metal, are considerably improved if the alkali metal or alkali metal-producing substance is added with or in the presence of a salt or compound having an acid reaction.

As compounds or salts having an acid reaction I may use any of the chemical substances of this nature and obtain the benefits of my invention. Among the substances which I particularly prefer to use are the bifluorides, the silicofluorides, and such easily fusible acids as boric acid. For descriptive convenience,tI will term this class of sub stances as compounds'having an acid reaction.

When a compound having an acid reaction is added to molten aluminum-silicon alloys with or in conjunction with an alkali metal, or an alkali metal-producing substance, hereinafter generally termed alkali metal, the deleterious effects heretofore noted as being produced in the metal casting by reason of the alkali metal treatment are largely overcome and the resulting casting is free from porosity and blisters. The beneficial effect of my new process is particularly noticeable when amounts of alkali metal larger than about 0.1 per cent by weight of the total melt are added. Moreover, by this method of modification, aluminum-silicon alloys of high silicon content, such as those containing as much as 35 per cent of silicon, are materially benefited. The method of this invention is, however, useful in the treatment of aluminum alloys containing as low as 3 per cent of silicon, and within the range of about 3 to about 35 per cent of silicon this novel method of modification is very useful.

The compound having an acid reaction may be added to the molten mixture together with the alkali metal or prior or subsequent to the addition thereof. While the exact beneficial effect of the addition of a compound having an acid reaction is not clearly known to me, I attribute its beneficial effect in producing a casting free from porosity or blister as caused by the tendency of the compoun to neutralize any alkaline reaction of the alkali metal added. The amount of the compound ion having an acid reaction which must be added to the melt in order to obtain the desired effeet is not large but, on the other hand, large amounts may be added without deleterious eflect. In general practice I prefer to use amounts corresponding to about 0.2 to 4: per cent of the total weight of the melt, but these limits are not critical, and larger and perhaps even smaller amounts may be added under varying conditions. Whereas heretofore it was considered that the addition of alkali metal to molten aluminum-silicon alloys in amounts more than about 0.1 per cent of the total weight of the melt was not advisable in that co-called over-modification was produced and the resulting casting was porous and blistered, I have found that if the alkali metal is added with or in the presence of the compound having an acid reaction, very large amounts of alkali metal may be added without the deleterious efiects heretofore noted. I

Having thus. described my invention, I claim: r a 1. lhe process of modifying aluminum base alloys containing silicon, comprising adding to the molten alloy a compound having an acid reaction, and an alkali metal.

2. The .process ofmOdifying aluminum base alloys containing 3 to 35 'per cent of silicon, comprising adding to the molten alloy a compound having anacid reaction, and an alkali metal.

. ALADAR PAGZ.

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